The present invention relates to switching circuits, and in particular, to circuits and methods for controlling a switching regulator.
Switching regulators are circuits that receive an input voltage and produce an output voltage having different characteristics than the input. Example switching regulators include AC to DC switching regulators and DC to DC switching regulators. AC to DC switching regulators receive an AC signal and transform the AC signal into a DC signal. DC to DC switching regulators receive a DC voltage and transform the DC voltage into another DC voltage. For instance, a DC-DC converter may receive a voltage (e.g., 5 volts) and output a higher voltage (e.g., 10 volts). These DC-DC converters are referred to as “Boost” converters. Other DC-DC converters may receive a voltage (e.g., 5 volts) and output a lower voltage (e.g., 2.5 volts). These DC-DC converters are referred to as “Buck” converters.
Switching regulators are advantageous because they have a high efficiency. In other words, the amount of power (i.e., voltage and current) received at the input of the switching regulator is efficiently transferred to the output of the regulator to generate transformed voltage or current. Typically, switching regulators include one or more switching devices, such as a switching transistor, that is turned on and off in a controlled manner to efficiently transfer energy into an energy storage device, such as an inductor. The characteristics of the switching signal are changed in a controlled manner so that the switching regulator performs as desired. This is often accomplished by monitoring a parameter at the input or output terminal of the switching regulator (such as voltage or current) and modifying the switching signal to maintain the parameter at a constant value.
In many applications it is desirable to monitor the input current to the input terminal of a switching regulator, and control the switching regulator using the input current as a parameter (e.g., alone or together with other parameters). However, one problem with monitoring the input current is that additional circuitry may be required to sense the input current. Additionally, it may be desirable to monitor the input current and control the switching regulator as other parameters, such as output current or output voltage, for example, change over time. The most common approach to monitoring the input current is to include a resistor at the input of the switching regulator. As the input current flows through the resistor and into the switching regulator input, a voltage will appear across the resistor. This voltage may be sensed and used as a control parameter corresponding to the input current to control the circuit. However, power is dissipated as the input current flows through the resistor. This results in an undesirable reduction in the efficiency of the switching regulator.
Thus, there is a need for improved techniques for determining the input current of a switching regulator. More generally, there is a need for improved techniques for controlling switching regulators. The present invention solves these and other problems by providing circuits and methods for controlling a switching regulator.